The present invention relates to devices for storing a liquid chemical substance which is used as a reactant in a chemical process, as well as to apparatus containing such a device.
In many industrial chemical processes, a processing chemical is stored in a container in a liquid state and the supply of processing chemical in the container is gradually exhausted as the liquid is converted to a vapor and expelled from the container.
According to one technique currently employed for converting such a processing chemical to a vapor, a fill gas is introduced into the container via an inlet opening at the top of the container. This fill gas creates a high pressure region above the processing chemical. The container is also provided with an outlet line having an outlet pipe which is immersed in the processing chemical and which leads, via a filter and appropriate valves, to a flow control device, such as a liquid mass flow controller. The flow control device delivers the processing chemical to a vaporizer, together with a carrier gas. Within the vaporizer, the carrier gas mixes with the processing chemical to produce a vapor which is then delivered to the processing station. The processing station may be composed of a process chamber whose interior is maintained at a low pressure that acts to draw the vapor from the vaporizer.
In apparatus of the type described above, both the vaporizer and the flow control device normally contain orifices of very small size, in the range of 0.001 to 0.030 inch diameter. These orifices can be easily clogged or blocked by particles contained in the processing chemical. These particles may be present in the processing chemical when it is initially supplied to the apparatus, or can be created by reactions occurring between the processing chemical and the fill gas. Such particles can also be constituted by precipitates resulting from normal decomposition or aging of the processing chemical, or can result from corrosion of the components through which the processing chemical flows. Since such particles would rapidly clog or block or restrict orifices in the flow control device and/or the vaporizer, the filter upstream of the flow control device is often an important component of such apparatus.
However, since the purpose of the filter is to trap particles, the filter itself gradually becomes clogged and after a certain period of use, the filter usually must be replaced. In current state-of-the-art apparatus, filter replacement is associated with a number of serious drawbacks and difficulties.
For example, in order to replace the filter, the apparatus is typically shut down, not only to allow removal of the used filter and installation of a fresh filter, but also because filter replacement is usually accompanied by a relatively lengthy purging operation during which associated carrier lines are re-filled with the desired composition of carrier gas and chemical.
Furthermore, the types of processing chemicals employed in such apparatus are generally highly corrosive and/or toxic. Therefore, the process of removing a used filter is complicated by the need to assure operator safety. Handling and disposal of used filters therefore presents special safety issues and adds to the cost of operating the apparatus.
The problems posed by the removal, handling and disposal of these used filters are generally greater than similar problems associated with the replacement of a container whose supply of processing chemical has been exhausted. Such containers are normally equipped with inlet and outlet valves that must be closed before a used container can be removed. Therefore, although removal of a used container and installation of a fresh container must be effected in a careful manner, the safety problems associated therewith are typically less severe than those associated with removal of a filter.
FIG. 1 is a block diagram illustrating a portion of conventional apparatus in which such a filter is provided. This apparatus includes a container 2, of a type commonly referred to as an ampule, which is a sealed container supplied with a quantity of a chemical substance 4 in the liquid state. The upper portion of the interior of container 6 defines a head space 6 which is coupled, via an inlet opening in the lid, or top wall, of container 2, to an inlet line containing a manual valve 10. The inlet line will be connected to conduct a fill gas which is introduced into head space 6 in order to place liquid 4 under pressure. An outlet pipe 12 extends into container 6 via an outlet port located in the top wall of container 2. Pipe 12 has an inlet end which is immersed in liquid 4, typically at a level close to the bottom of container 2. Liquid chemical substance 4 is delivered to a vaporizer via pipe 12, manual valve 16, pneumatically-controlled valves 18 and 20, and filter 22. Valves 10 and 16 are typically secured to container 2 in a manner to be removed together with container 2 at the time of container replacement. Couplings 62 and 64 may be decoupled to permit removal of container 2 and valves 10 and 16. Prior to removal, valves 10 and 16 are closed and couplers 62 and 64 are purged by means of purge gas and vacuum lines 23a, 23b and 23c.
The flow path which includes valves 18 and 20 and filter 22 is further bridged by a bypass valve 24 which permits the filter 22 to be bypassed if necessary to maintain operation while the filter is replaced. The bypass line of valve 24 may similarly have a filter (not shown) to filter the flow while the other filter is being replaced. Prior to replacement of filter 22, valves 18 and 20 may be closed. The filter 22 may then be purged by passing a purge gas through the filter from a purge gas line 26a coupled to the filter. The purge gas and chemical residue is withdrawn through a vacuum line 26b.